Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art ignite injections of fuel to produce heat. In one example, fuel or a mixture of fuel and air injected into a combustion chamber of the engine is ignited by way of a spark plug. The heat and expanding gases resulting from this combustion process may be directed to displace a piston or move a turbine blade, both of which can be connected to a crankshaft of the engine. As the piston is displaced or the turbine blade is moved, the crankshaft is caused to rotate. This rotation may be utilized to directly drive a device such as a transmission to propel a vehicle, or a generator to produce electrical power.
During operation of the engine described above, a complex mixture of air pollutants is produced as a byproduct of the combustion process. These air pollutants are composed of solid particulate matter and gaseous compounds including the oxides of nitrogen (NOx). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of solid particulate matter and gaseous compounds emitted to the atmosphere from an engine is regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to reduce the production of these pollutants is to introduce a lean air and fuel mixture into the combustion chambers of the engine. This lean mixture, when ignited, burns at a relatively low temperature. The lowered combustion temperature slows the chemical reaction of the combustion process, thereby decreasing the formation of regulated emission constituents. As emission regulations become stricter, leaner and leaner mixtures are being implemented.
Although successful at reducing emissions, very lean air and fuel mixtures are difficult to ignite. That is, the single point arc from a conventional spark plug may be insufficient to initiate and/or maintain combustion of a mixture that has little fuel (compared to the amount of air present). As a result, the emission reduction available from a typical spark-ignited engine operated in a lean mode may be limited. In addition, conventional spark plugs suffer from low component life due to the associated high temperature of the localized arc.
One attempt at improving combustion initiation of a lean air and fuel mixture while minimizing component damage is described in U.S. Pat. No. 4,726,336 (the '336 patent) issued to Hoppie et al. on Feb. 23, 1988. The '336 patent discloses a laser ignition that can be used with an internal combustion engine having a pre-chamber. The pre-chamber has a combustion space, which is connected to a main combustion chamber of the engine via overflow openings. The pre-chamber is supplied with fuel from a separate feed line. Instead of a spark plug, a combustion window made of sapphire is provided in a side wall of the pre-chamber, and laser light is passed from a focusing lens through the window into the center of the pre-chamber to initiate combustion therein. The laser light pulses at different levels for short time intervals per an ignition procedure. The multiple pulses of laser light permit real-time adjustment of light intensity such that, if a first pulse does not lead to ignition, the intensity of a second pulse is increased. In this manner, a reliable ignition can be efficiently achieved even with very lean air and fuel mixtures, without detriment to the laser ignition.
Although the ignition of the '336 patent may improve combustion of a lean air and fuel mixture and may have an affect on the damage caused by high temperature arcing (i.e., by eliminating arcing altogether), the ignition may still be problematic and have limited applicability. For example, the amount of light energy and the size and complexity of the laser optics required to ignite the air and fuel mixture may be at least partially dependent on the volume of the mixture. That is, a large combustion chamber volume may require a large amount of power and high energy levels directed to many different locations to sufficiently ignite the mixture within the chamber. Thus, although the ignition of the '336 patent may, in one embodiment, be coupled with a smaller pre-chamber to reduce the laser energy required for ignition, the requirements may still be difficult to satisfy. And, in engines without pre-chambers, the ignition of the '336 patent may require prohibitively expensive optics to generate multi-point ignition similar to that achieved within a smaller pre-combustion chamber.
The igniter of the present disclosure solves one or more of the problems set forth above.